Technical Abstract:
In June of 2012, an outbreak of highly pathogenic avian influenza (HPAI) H7N3 was reported poultry in Jalisco, Mexico. Since that time the virus has spread to the surrounding States of Guanajuato and Aguascalientes and new outbreaks continue to be reported. To date more than 25 million birds have died or been slaughtered in an effort to stop the spread of disease. In response to the outbreak, vaccine efficacy trials were performed to determine if U.S.- and Mexican-origin inactivated H7 vaccines would protect birds from clinical disease and reduce shedding of virus. In the first set of experiments, four U.S. H7 low pathogenic avian influenza (LPAI) isolates were formulated into inactivated emulsion vaccines and injected into 7 week old specific-pathogen-free (SPF). These isolates contained between 92-97 % amino acid similarity to the hemagglutinin gene of the Mexican HPAI challenge virus (A/chicken/Jalisco/CPA1/2012 H7N3). The APHIS-approved H7 vaccine antigens were included into this experiment for testing. Birds were challenged at 10 weeks of age with 106 EID50 per bird delivered via intranasal route. Results demonstrate that three of the four H7 vaccine isolates tested provided 100 % protection, whereas the fourth isolate provided 90 % protection. In the second experiment, a Mexican-lineage LPAI H7N3 isolate from a duck, with 98 % sequence similarity to the HPAI virus, was formulated into an inactivated vaccine and applied to 2 week old chickens. Birds were challenge as previously described and demonstrated 100 % protection from challenge. All vaccines tested reduced shedding of virus compared to sham vaccinated birds. Taken together, these results indicate that both U.S. and Mexican vaccine isolates can provide protection to poultry against this recent HPAI H7N3 virus.